JP3036688B2 - Method for replacing lower furnace internal structure assembly and apparatus for aligning position of core vessel - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nuclear reactor, and more particularly to an apparatus and a method for replacing internal components such as a lower reactor internal structure of a nuclear reactor.

[0002]

2. Description of the Related Art In a nuclear reactor, internal components are typically composed of an upper internal structure and a lower internal structure. The upper reactor internals include a control rod guide tube assembly, a support post, an instrumentation conduit that extends through the closed head and into the reactor vessel, and a fuel assembly position alignment structure referred to as an upper core plate. including. On the other hand, the lower reactor internal structure includes a core support structure called a core tank, and an instrumentation conduit extending from the bottom of the reactor vessel into the reactor vessel. After many years of use,
A situation often arises in which it is desirable to replace a portion of the reactor internals, especially the lower internals proximate the core. Such exchanges can be caused by vibrations that occur during operation of the reactor,
Replacing components exposed to radiation and thermal stress with new components not only could extend the life of the reactor, but also improved after the reactor was first assembled at the factory. It is also possible to introduce equipment. For example, by employing improved shielding in the core baffle area so that more fast neutrons are reflected back into the core, not only can fuel efficiency be increased, but also the life of the reactor vessel is increased. can do. In the past, despite the benefits of replacing the lower furnace internals, such replacement was considered impractical during a refueling outage. The reason for this is that in order to ensure proper operation of the reactor, the new lower core structure must be accurately aligned with the existing upper core structure and pressure vessel. In previous attempts, such precise alignment or alignment required extensive on-site work to align the new lower core structure with the existing upper core structure and pressure vessel. Is required. As a result of this on-site work, (i) reactor outage time not only increases unacceptably beyond the time associated with refueling work, but May be excessively exposed.

[0003]

Accordingly, the replacement of lower reactor internals in a nuclear reactor in a relatively short period of time and with minimal radiation exposure of workers is a new component to existing ones. There is a need for an apparatus and method that allows for replacement while ensuring accurate alignment of the components.

[0004] It is an object of the present invention to provide an apparatus and a method for replacing a lower internal structure in a nuclear reactor.

[0005] It is a further object of the present invention to provide a new lower reactor interior to existing pressure vessels and upper reactor internals without unduly increasing reactor downtime and / or operator radiation exposure. It is an object of the present invention to provide a method and apparatus for properly aligning or aligning a structure.

[0006]

SUMMARY OF THE INVENTION The above and other objects are attained in a method of replacing a previously used lower core assembly in a reactor pressure vessel with a replacement lower core assembly. , A first position alignment means is formed
In Rubeki position, measuring the position of alignment with the lower internals assembly and said pressure vessel above replacement remotely, the pressure vessel and the lower for the replacement based on measurements of the remote position alignment Forming said first alignment means such that a predetermined alignment with the furnace internals assembly is achieved.
The first step of remotely measuring or determining the alignment of the replacement lower core structure assembly may be performed using the actual lower core structure assembly or, in an equivalent implementation, simulated. It can also be carried out using the lower furnace internal structure assembly.

In a preferred embodiment, the above and other objects include (i) a pressure vessel, (ii) a core containing a fuel assembly, (iii) a control rod drive shaft, and (iv) a control rod drive shaft. A reactor comprising: an upper reactor internal structure assembly adapted to support the control rod drive shaft; and (v) a lower internal structure assembly supported by the pressure vessel to support the core. Achieved. Here, the upper core assembly is provided with two alignment pins for each fuel assembly to align, ie, align, the fuel assembly with the upper core. Including the upper core plate. The lower furnace internals assembly is comprised of a core vessel with two position alignment devices. The first alignment devices each include a support key adapted to engage a keyway formed in the pressure vessel for aligning the lower furnace structure with respect to the pressure vessel. .
Proper alignment of the lower furnace internals with respect to the pressure vessel
This is achieved by setting the gap between the radial support key and the side surface of the keyway to a predetermined size after properly disposing the lower furnace internal structure in the pressure vessel. A second alignment device includes an alignment pin adapted to engage a notch formed in the upper core plate to align the lower core structure with the upper core structure. including. Proper alignment of the lower core structure with respect to the upper core structure is formed on the alignment pins and the upper core plate after the upper core plate is properly positioned above the lower core plate and relative to the cavity in the core vessel. This is realized by setting the gap between the notch and the side of the notch to a predetermined size.

The replacement of the existing lower core structure with a new, properly aligned lower core structure is adapted to accommodate the keyways of the existing pressure vessel and the cutouts of the existing upper core plate, respectively. In addition, this is achieved by matching the position and size of the radial support keys and alignment pins in the new lower furnace internals. The radial support key is aligned by using remote means to determine the location of the key centerline on the new lower furnace internals required to achieve the predetermined alignment. This is achieved by attaching a first gauge having an extendable plunger to the new lower furnace internals at the support key and placing the new lower furnace internals in the vessel. In this case, the plunger tip is then extended until it contacts the side of the keyway, and the required distance from the key center line to the keyway is determined using the extended distance. This measurement, which is performed by mechanical or electronic means, can be performed once the new lower furnace internal structure is removed. Next, the key for the new lower internal structure is aligned and ground so that the above-mentioned alignment is achieved.

The position alignment of the new lower core structure with respect to the existing upper core structure is performed so that a desired gap is obtained between each pin and a side of a notch provided in the upper core plate. This is performed by providing holes for alignment pins on the side of the tank. This involves placing a second gauge with a telescoping plunger on the underside of the existing upper core plate and using two of the fuel assembly alignment pins near the notch to achieve the second gauge. This is achieved by positioning the gauges. When the plunger is extended to fix the notch and fixed to that position, and attached to a new lower furnace internal structure, the projection sets the center line of the opening that becomes the center line of the alignment pins of the upper core plate. Another feature of this gauge is that it is positioned below the gauge plate in a fence-like arrangement that is precisely positioned with respect to the fuel assembly alignment pins and represents the perimeter or boundary of the core vessel cavity, very close to the notch in the upper core plate Protruding additional pins are provided. The gauge is positioned and mounted at each of the four notch locations on the upper core plate, which are located at 0 °, 90 °, 180 ° and 270 °.
Identified as a location. Holes on the gauge plate,
Once the center of the notch has been created by a score line or other suitable method, these four gauges are sent to the factory where the new reactor internals are being manufactured. The gauge is then attached to the dummy upper core plate above the correctly positioned alignment pins for the dummy fuel assemblies, as on the old upper core plate. In this way, the gauged dummy core plate is then positioned at the appropriate height in the new lower core vessel and supported on top of the core baffle structure. Then, the dummy core plate is rotated and moved until an optimum position is achieved with respect to the baffle cavity opening and the lower core plate. Mark on the gauge indicating the center of the notch on the actual core plate (hole, notch or scribe line)
Is transferred to the lower core tank. In this way, the exact position for drilling the holes for the alignment pins of the upper core plate is determined.

In setting the axial center line of the alignment pins of the upper core plate in a new core tank,
As a best practice, first drill holes in the core vessel at the theoretically correct centerline location. (This hole may be smaller in size compared to the final hole size in which the alignment pin is mounted). By working radially through this hole, the center line of the notch for the alignment pin of the dummy core plate is displayed. The center line of the smaller hole is then transformed to coincide and the hole is ground to this newly set center with the final dimensions. This operation is repeated at each of the four upper core plate alignment pin positions.

[0011]

FIG. 1 shows a nuclear reactor which can be used in a nuclear power plant. The reactor has a substantially cylindrical pressure vessel 1 sealed at its top by a substantially hemispherical lid 2. A core 71 is arranged in the pressure vessel 1. The core 71 is constituted by an array of rectangular fuel assemblies 14. Although only four fuel assemblies 14 are shown in FIG. 1 for simplicity of illustration, in practice, the number of fuel assemblies is very small as can be imagined from the arrangement shown in FIG. Is a large number. The core tank 5 is also arranged in the pressure vessel 1 and surrounds the core 71. The core tank 5 includes a substantially hemispherical bottom 11, a heat shield 6 surrounding a cylindrical portion 72 near a core 71,
It comprises a lower core plate 9 on which the fuel assemblies 14 are mounted, a diffuser plate 10, and a baffle 17 surrounding the fuel assemblies 14 and fixed to a cylindrical portion 72 via a former 70. Here, the core shown in FIG. 1 is a typical example of a nuclear reactor to which the present invention can be practically applied, but the present invention relates to, for example, as in some recent nuclear reactors, The bottom part 11 is forged in a flat shape, and a series of pads directly bolted to the core tank at a location where neutron leakage is large is used in place of the cylindrical heat shield 6, instead of the baffle 17 and the former 70. FIG. 1 shows that an integral core reflector can be used for
It is clear that the present invention can be similarly applied to a nuclear reactor having a structure slightly different from that shown in FIG.

As shown in FIG. 1, a plurality of instrumentation thimble guides 13 extend through the bottom of the pressure vessel 1 and through the bottom 11 of the core vessel 5 into the core 71. Further, an energy absorber 85 including the plate 12 fixed to the support column 60 is fixed to the bottom 11 of the core tank 5. The role of the energy absorber 85 is to absorb a part of the impact load when the upper flange of the core vessel is damaged and the core vessel 5 falls to the bottom of the pressure vessel 1.

The components within the pressure vessel 1 described above are generally referred to as "lower furnace internals" assemblies. In contrast, the “upper furnace internals” assembly includes an upper core plate 8, a control rod support plate 56, and a column 4 (only two columns 4 are shown in FIG. And a control rod guide tube 52 for each control rod drive shaft 3, and an instrumentation thimble guide (not shown) extending between the plates 8 and 56. FIG. 1 shows only two control rod drive shafts 3 for the purpose of simplifying the illustration,
In practice, as implied in FIG. 2, the number of control rods is a very large number. Also, the illustration of the instrumentation thimble guide is omitted.

In operation, coolant flows into inlet nozzle 15. Although only one inlet nozzle 15 is shown in FIG. 1, the inlet nozzles 15 are distributed and arranged around the circumference of the pressure vessel 1. The coolant flowing into the inlet nozzle 15 flows downward in the annular passage between the core tank 5 and the pressure vessel 1. The coolant then flows to the bottom 1 of the core vessel 5.
1 flows into the core tank 5 through a hole (not shown) formed in the core 1 and flows upward through the core 71 to absorb heat. The coolant then exits the core via hole 74. The holes 74 are formed in the upper core plate 8, but only two holes 74 are shown in FIG. From the core plate 8, the coolant is discharged from the core tank 5 through a discharge port 73. The outlet 73
Although only one is shown in FIG. 1, they are distributed along the circumference of the core tank. The coolant flowing out of the core tank 5 then flows out of the reactor via the outlet nozzle 16. The outlet nozzles 16 are also distributed along the circumference of the pressure vessel 1 and are aligned with the outlet 73 of the core vessel.

In order for the nuclear reactor to function properly, a certain exact arrangement or alignment must be maintained between the pressure vessel 1, the upper furnace internals and the lower furnace internals. Vertical alignment, i.e., alignment along the longitudinal axis of the reactor, is achieved with the vessel flange 57. As shown in FIGS. 1 and 12, a flange 58 formed on the top of the core vessel 5 rests on a support surface formed on the flange 57 of the pressure vessel, so that the core vessel is pressurized. It is vertically aligned with the container. The upper furnace internal structure is
The control rod supporting plate 56 is vertically aligned with the lower furnace internal structure and the pressure vessel 1 by the flange 59 formed on the control rod support plate 56. As shown in FIG. 1 and FIG.
9 is a holding spring 7 mounted on a flange 58 of the core tank.
7 on.

As shown in FIGS. 1 and 12, a pressure vessel,
The horizontal alignment between the upper core structure and the lower core structure, that is, alignment along a plane perpendicular to the longitudinal axis of the reactor, is set at the top of the core vessel 5. This alignment is done with screw 7
8 and the control rod support plate flange 59 and the pressure vessel flange 5, respectively.
7 by a lid / pressure vessel alignment pin 50 that extends into notches 75 and 76 formed in FIG. This alignment is achieved by assembling the pins 50 and notches 75 and 7 during assembly.
Checked by measuring the gap between the six. Typically, the gap between the pin 50 and the notch 75 is about 0.4
At 1 cm (0.016 in), the gap between pin 50 and notch 76 should be about 0.032 cm (0.032 in). Four pins 50 are arranged along the circumference of the core tank flange 58 so that proper alignment is achieved in each direction along a plane perpendicular to the longitudinal axis of the reactor.

The core vessel 5 is also aligned with the pressure vessel 1 at the bottom 11 by a radial support key 32, as shown in FIG. A specially grounded insert member 36 having a keyway 35 formed therein is disposed in a slot formed in a boss 38 projecting radially from the inner surface of the pressure vessel 1. A key 32 fixed to a mounting pad 39 formed on a boss 37 projecting radially from the outer surface of the bottom 11 of the core tank engages with the key groove 35, thereby connecting the core tank 5 to the pressure vessel 1. Align.

The correct alignment of the core vessel 5 requires that the core vessel 5 in the pressure vessel 1 be properly inserted into the notch 76 formed in the flange 57 of the pressure vessel at the initial stage of the assembly. Achieved by positioning such that, when engaged, the radial gap between the outlet 73 provided in the core vessel and the outlet nozzle 16 of the pressure vessel is equal along the circumference of the reactor. Is done. This alignment is set by specially grinding each insertion member 36 for each reactor so that an appropriate gap is obtained between the side surfaces 61, 62 of the key 32 and the side surfaces 63, 64 of the key groove 35. You. Typically, the gap is 0.038 cm
(0.015 in). In all directions on a plane perpendicular to the longitudinal axis of the reactor, six keys and key grooves as described above are formed along the circumference of the core vessel 5 and the pressure vessel 1 to ensure proper alignment. I have. However, some plants are provided with four such keys and keyways. It should be noted that the base of each key 32 is fixed to the mounting pad 39 by a screw 33, the position of which is accurately maintained by the dwell 34.

Proper alignment of the upper core structure with respect to the lower core structure is achieved by aligning the four upper core plates arranged along the circumference of the core vessel 5 as shown in FIGS. This is realized by the pin 18. As shown in FIG. 3, each pin 18 passes through a hole 79 formed in the core tank,
It extends into a notch 19 formed in the periphery of the upper core plate 8. In each notch 19, an insert 20 ground to each reactor is mounted so that a small gap can be obtained between the side of the notch 19 and the pin 18. Typically, this gap is about 0.015 during assembly.
cm (0.006 in).

As shown in FIGS. 1 and 2, the fuel assembly 14 is provided with the alignment pins 7 provided on the upper core plate 8.
Aligned with the upper furnace internals. Each fuel assembly 14
, Two pins 7 are used. Each pin 7 extends into the fuel assembly through a hole 26 formed in the upper core plate 8 as shown in FIG. According to the present invention, the time during which the reactor is shut down and maintenance personnel are exposed to radioactivity in order to replace the lower reactor internals and achieve the above-described alignment is provided by the method and apparatus described below. It can be minimized by using it.

As shown in steps 88 to 91 in FIG. 14, the reactor cavity 54 shown in FIG. 13 is filled with water before removing the upper and lower internal structures from the pressure vessel 1. Mounting pad 3 instead of radial support key
9 a radial support key gauge 40 attached to
Is used to align the new core vessel 5 with the pressure vessel 1 at the radial support key 32 by placing the new core vessel 5 in the pressure vessel 1. By using the gauge 40, the alignment of the new core tank 5 with respect to the pressure vessel 1 is determined remotely. That is, a maintenance worker is required without having to physically approach the key / keyway area. Based on the information obtained in this way, in the next step, the radius for the core tank required to realize proper alignment, that is, to obtain the above-mentioned gap between the key and the keyway 35 is obtained. The position of the radially extending portion 51 of the direction support key 32 is determined. In that case, a new radial support key 32
Is modified so that its radially extending portion 51 is in an appropriate position when the key is dwell-fixed to the core vessel.

In this way, in step 92, as shown in FIG. 9, the new core vessel 5 is pressurized so that the radial support key gauge 40 is mounted on each of the six radial support key mounting pads 39. Lower into the container. The dowel 34, which extends into a hole formed in the base 80 of the gauge 40, allows the gauge to be accurately mounted on the mounting pad 3.
9 serves for positioning. Referring to FIG.
Linear voltage operated transformers (hereinafter also referred to as LVDTs)
41 is mounted in a hole 42 provided on the side of the gauge 40. FIG. 11 shows only two of the six transformers. The lead wire of the LVDT 41 is pulled out of the gauge through a vertical hole 44 that passes through the gauge.

When lowering the core tank 5 into the pressure vessel 1,
The voltage applied to each LVDT 41 is maintained such that the tip of the plunger 43 of the LVDT maintains a retracted position in which the tip of the plunger 43 is flush with the surfaces 67 and 68 of the gauge 40. 8 and 9
As can be seen from the comparison, the thickness of the portion of the gauge 40 extending in the radial direction is set smaller than the thickness of the radial support key 32 so that the gauge can easily fit into the key groove 35. After the core tank flange 58 is seated on the pressure vessel flange 57 and the core tank 5 is properly aligned with the pressure vessel 1, the voltage applied to each LVDT 41 is
It increases until the plunger contacts the sides 63, 64 of the keyway 35. In that case, the expansion and contraction movement of the plunger can be remotely monitored by an underwater television camera 49 as shown in FIG. , 64
Is ensured to contact the

By measuring the change in the voltage supplied to the LVDT 41, the distance traveled by the plunger of the LVDT, and thus the keyway 3 from each face 67, 68 of the gauge 40, is measured.
The distance to each side 63, 64 of No. 5 can be determined. The combination of the distance determined in this manner and the thickness of the radially extending portion of the gauge 40 measured in a conventional manner forms the boss 37 from the width of the key groove 35 and the center line 66 of the key groove. The distance to the dwell hole 81, that is, the dimension E shown in FIGS. 8 and 9 can be obtained.

Using the data obtained as described above, a new lower furnace internal structure is created in step 102 in FIG.
As shown in the above, modifications can be made on site to suit the reactor structure. Such a modification is achieved by modifying the six new radial support keys such that each of the six new radial support keys 32 specifically engages a respective keyway 35. In this modification method, the key is formed such that (i) the thickness of a radially extending portion of the key is:
About 0.038 cm as described above between the key and the side of the keyway
(Ii) a gap from the center line of the radially extending portion of the key to the dowel hole 69 formed at the base of the key and used to position the key. As shown in FIG. 8, the keys are individually machined so that the center line of the key and the center line 66 of the key groove coincide with each other.

Although the above procedure has been described in connection with a key / keyway alignment device, the present invention also engages with other alignment devices, such as a hub formed on the inner diameter of the pressure vessel 1. Obviously, it is equally suitable for use with other alignment devices such as radial contact pads distributed around the periphery of the core vessel 5. Also, the keyway 3 from the gauge 40
The preferred embodiment for remotely measuring the distance to the side of 5 was to use the LVDT 41, but this measurement was, for example, mechanically stretched with a thread,
It is also possible to use a mechanical means such as a pin fixed in a predetermined position by a set screw, and to use a mechanical means capable of measuring the length of the pin after removing the core vessel 5 from the pressure vessel 1. Will.

FIGS. 15-17 show that important measurements are made in the pressure vessel using gauges that simulate important features on the replacement internals without using the new lower furnace internals as gauges. 1 illustrates one embodiment of a process for performing the above. This feature of the invention opens up great possibilities for replacement of lower furnace internals.

(1) The measurement of the candidate vessel (also referred to as gauging) is performed by removing the lower furnace internal structure from the pressure vessel and installing it in a storage stand, such as during a planned in-service inspection. Can be performed while the operation is stopped. With the lower furnace internals installed on the storage stand, the flange seating surface of the core tank and the energy absorber (Fig. 1)
(Indicated by reference numeral 12) can also be measured using conventional methods. The replacement internals can be completely manufactured while the plant is in operation. If the replacement is scheduled, the downtime is considerably reduced since the new lower furnace structure is ready for installation at any time.

(2) Some new lower furnace structures completed with the lower radial support key may already exist (perhaps from the cancellation of plant construction). In that case, using the pressure vessel dimensions measured using the simulated lower furnace internals gauge, the lower radial support key, so that it can be mounted as desired within the pressure vessel, The outlet of the energy absorber and the core tank can be changed. Also in this case, if the replacement lower furnace internal structure having completed all the changes has arrived at the site of the plant, it is possible to reduce the operation stoppage time of the plant.

FIG. 15 shows two outlet nozzles 15 and 16
A simulated lower reactor, located within the reactor vessel 1 having four lower radial supports ( represented by one outlet nozzle 15 and one inlet nozzle 16) and bosses 38 1 shows a structure gauge 200. FIG.
As shown, the gauge 200 is used in place of the four gauge blocks 140 (the gauge 40 shown in FIGS. 9 and 11) that simulate the lower radial support key 32 shown in FIGS. ) And four gauge pins 150 that simulate the lid / pressure vessel alignment pin 50 shown in FIGS. The gauge 200 also includes two simulated outlet nozzle connections 115 adjacent the outlet nozzles 15 and 16 of the pressure vessel.
And 116 and a simulated energy absorber substrate 112. These simulated parts of the gauge 200 are supported by a rigid main frame 202. The main frame 202 includes four horizontal members 206 extending from an upper plate assembly 208 for supporting the gauge pins 150 and simulated outlet connections 115 and 1.
Four horizontal members 210 (only two of which are shown) extending from an intermediate plate (represented by one connection 115 and one connection 116) assembly 212 for supporting the 16 Four horizontal members 214 extending from lower plate assembly 216 for supporting block 140
It is composed of These horizontal structural members are reinforced by a central hollow column 220 and four vertical members 222. Each of the vertical members 220 and 222 may be manufactured from several flanged short members, as shown, or alternatively may comprise one long member.

Simulated energy absorber substrate 11
2 is a view showing the gauge 200 as shown in FIG.
It is attached to the lower end of the vertical column 230 so that it can slide with respect to the central hollow column 220 when placed inside.
The vertical column 230 is a hollow column 22 having the vertical column 230 as a center.
2 to guide the vertical column 230 when exercising within 0
Two large diameter portions 232 and 234 and a lower plate assembly 216
And a hole (not shown) provided therein. Here, the large diameter portion 234, which is the lower guide portion, is
0 restricts the relative vertical movement of the simulated energy absorber substrate 112 with respect to the main frame 202 as it moves between the reactor vessel 1 and the stand 236 (shown in FIG. 17). It is preferably larger than the holes provided in the holes. The main frame 202 also has a lifting rig 240 for transporting the gauge 200 and support legs 242 that provide support on a stand 236.

The gauge block 140 is adapted to extend radially into the keyway 35 of the pressure vessel shown in FIG.
00 on the main frame 202. The gauge block 140 can be equipped with the LVDT 41 shown in FIG. 11 and the measurements are made in the same way as with the new lower furnace internals so as to obtain basic data on these keyway gauges or dimensions. be able to. The four pins 150 are positioned on the theoretically true center line of the upper part of the gauge to simulate the lid / pressure vessel alignment pin 50 shown in FIG.
However, the gauge pin 150 does not correspond to the gap 76 shown in FIG.
However, it is advantageous to fit the keyway of the pressure vessel so as to be about 0.006 inch (0.152 mm) instead of the designed value of 0.032 inch (0.813 mm) for each side. The simulated lower furnace structure gauge 200 can be in a raised position and supported on the flange surface of the pressure vessel where the flange of the lower furnace structure assembly sits. What is important here is that the gauge block 140 is located above the pin 150 on the same horizontal center line as the pin 150. When measuring the gap in the key groove 76 of the pressure vessel, the center line of the key 66 is aligned with the pin 150 in the pressure vessel 1.
Can be set with respect to the center line of the key groove 76 occupied by. In that case, when converted to a replacement lower furnace structure, the lower radial support key 32 would be aligned with the lid / pressure vessel alignment pin 50 in the same relationship as pressure vessel measurements showed. In addition, it can be assembled (or modified if already assembled) to match the lid / pressure vessel alignment pins 50 with a gap specified by the design engineer. (Instead of using the LVDT 41 as a keyway measuring device for the pressure vessel, a gauge block (not shown) ground to completely fill the keyway with a clearance sufficient only to allow engagement can be used. Instead of fixing these blocks to the simulated lower furnace internals gauge 200,
It can be moved (remotely) along the gauge surface and dropped into the keyway of the pressure vessel to lock in place. )
When removing the gauge 200 from the pressure vessel 1, the gauge 200 is placed on the reactor cavity work deck, brought to a level position, and then with respect to the center of the gauge block relative to the simulated lid / pressure vessel alignment pin 150. A measurement can be made. These measurements are
This can be achieved using simple means such as an optical / target sighting device using a theodolite sighting scope or a wire plunger 250 suspended within the gauge 200 from the center of each simulated lid / pressure vessel alignment pin 150. it can. See FIG. 17 in this regard.
The offset of each lower radial support key relative to the lid / pressure vessel alignment pin 150 on the core tank flange can then be set on the new lower furnace internals.

As already mentioned, in addition to aligning the new core vessel 5 with respect to the pressure vessel, a new core vessel is
The upper core plate alignment pins 18 must be aligned with the upper core internals. According to the present invention, this alignment is achieved by determining the position of the notch 19 provided in the upper core plate 8 with respect to the fuel assembly 14. Since the fuel assembly is removed during the alignment operation, the position of the notch with respect to the fuel assembly is not directly determined. Instead, the fuel assembly alignment pin holes 26
Find the position of the notch with respect to. The reason is that the positions of the fuel assembly alignment pin holes 26 indicate the positions of the fuel assemblies. Then, using this information, the holes 7 for holding the alignment pins 18 are used.
The hole 79 is pierced in a new core vessel 5 with the position of 9 being determined. This approach ultimately ensures that the fuel assemblies are properly centered in the baffle 17 of the new core vessel 5.

The notch position is determined in step 94 in FIG. 14 after the upper furnace internal structure is taken out of the pressure vessel in step 89 in FIG. The position of the notch 19 is obtained by attaching an alignment pin gauge 25 to the lower surface of the upper core plate 8 at the position of each notch as shown in FIG. As shown in FIGS. 5 and 7,
The gauge 25, two holes 31 ₁ and 31 ₂ are formed in the small gap. These holes are spaced to coincide with the _two fuel assembly alignment pin holes 26 ₁ and 26 ₂ provided in the upper core plate. This allows the two fuel assembly alignment pins 7 ₁ and 7 ₂ to extend into the holes 31 ₁ and 31 ₂ , respectively, so that the gauge can be accurately positioned on the upper core plate 8. . Three leveling pads 27 (two of which are shown in FIG. 7) ensure that the gauge rests on the lower surface of the upper core plate 8.

The alignment pin gauge 25 is attached to the upper core plate 8 such that the tongue 28 projecting from the gauge enters the notch 19 as shown in FIGS. When the two setscrews 30 provided on the tongue 28 are loosened and the plungers 29 located on both sides of the tongue are released, the spring 82 causes the plunger to notch 1
9 is driven to abut against the side of the horn 9. Next, the set screw 30 is tightened to fix the plunger 29 and the gauge 25
From the upper core plate 8. The position of the center line 83 of the notch 19 against the hole 31 ₁ and 31 ₂ provided on the gauge 25, shown as dimension A and C (i) Figure 5, until the hole 31 closest to the tip of the plungers 29 And (ii) the distance between the tips of the plungers, shown as dimension B in FIG.

The measurement results obtained as described above are transferred to the dummy core plate 21 shown in FIG. here,
The dummy core plate 21 has a plurality of holes 22 having the same size and shape as the upper core plate 8 and having the same size as the fuel assembly alignment pin holes 26 formed in the upper core plate. . Although the number of holes 22 provided in the dummy core plate 21 is smaller than the number of fuel assembly alignment pin holes 26 provided in the upper core plate 8, each alignment pin hole 22 has the outermost fuel assembly alignment. It corresponds to one of the pin holes 26, ie, one of the alignment pin holes 26 closest to the periphery of the upper core plate. The position of each alignment pin hole 22 with respect to the dummy core plate 21 is the same as the position of the corresponding fuel assembly alignment pin hole 26 with respect to the upper core plate 8. Therefore, in practice, the alignment pin holes 22 formed in the dummy core plate 21 form a pattern that matches the periphery of the assembly of the fuel assemblies 14 forming the core plate 21.

Dimensions A, B and C obtained as measured values
And transferred to the dummy core plate 21, as shown in FIG. 4, the corresponding gauge 25 to pins 7 ₁ and 7 two holes _{26 2} by inserting the ₁ and 26 ₂ for attachment to the upper core plate 8 hole 22 to ₁ and 22 ₂ used to determine the position of the center line 23 of the cutout 19. Dummy core plate 2 along center line 23
A hole 24 is drilled in 1 and used as a reference point for drilling a hole 79 for the alignment pin 18 as described below. Each of the positions of the four notches 19 in the upper core plate is such that the dummy core plate 21 has four holes 24 corresponding respectively to the positions of the notches 19 with respect to the fuel assembly alignment pin holes 23. Is repeatedly executed.

Next, the dummy core plate 21 is placed in a new core tank 5 as shown in FIG. That is, the dummy fuel assembly alignment pins 84 inserted into the holes 22
Are positioned in the core tank 5 such that the core plates 21 are equally spaced from the baffle 17. Then, using the hole 24 as a reference point, as shown in step 102 of FIG. 14, an alignment pin hole 79 is drilled in the core tank 5 as a part of individually aligning a new lower furnace internal structure.

The above approach has two important features.
First, the holes 22 ₁ and 22 ₂ used to position the holes 24 correspond to the holes 26 ₁ and 26 ₂ used to align the fuel assembly 14 with respect to the upper core plate. Second, the holes 7 through which the alignment pins 18 pass are formed.
9 is to be positioned by centering holes 22 ₁ and 22 ₂ with respect to baffle 17. Thus, according to the above-described method, the fuel assembly 14 is placed in a new core tank 5 and the alignment pins 18 are inserted into the cutouts 19 formed in the upper core plate, whereby the upper core plate is removed. The fuel assembly is properly aligned with respect to the baffle 17 by the fuel assembly alignment pins 7 provided on the baffle 17. It should be noted that the gap between the baffle and the fuel assembly is only about 0.16 cm (0.06 in), and therefore careful alignment is required.

In accordance with the present invention, the alignment measurements performed on the existing upper core plate 8 using the dummy core plate 21 include the refueling operation prior to shutting down the lower core structure. This can be done during shutdowns, thereby saving a very large amount of time compared to shutting down the lower furnace internals.

In order that the energy absorber 85 shown in FIG. 1 can properly absorb the impact when the core vessel falls to the bottom of the pressure vessel 1, the energy absorbing plate 12 and the bottom of the pressure vessel can be properly absorbed. About 2.84cm (1.12i) between the inner surface
Maintain gap n). To obtain this gap, the length of the support column 60 of the energy absorber 85 is adapted to the new core vessel 5 itself. In order to adapt this new core vessel 5 itself, it is necessary to accurately measure the distance between the core vessel bottom 11 and the pressure vessel bottom.
According to the invention, this measurement can be achieved by slidably mounting the gauge 46 in a new core vessel as shown in FIG. As shown in FIG. 10, a scratch gauge 47 and a dial gauge 48 are attached to the gauge 46. When the core vessel is lowered into the pressure vessel at step 92, the bottom of the gauge 46 contacts the bottom of the pressure vessel and the gauge slides up the core vessel. The dial gauge 48 is remotely observed by the underwater television camera 49. When the core tank flange 58 is properly seated on the pressure vessel flange 57, the gauge 46 reads the pointer on the dial gauge 48 which indicates the distance that the gauge slid up the core tank. The scratch gauge 47 permanently records this display reading amount as backup data. The distance D between the bottom of the core tank and the bottom of the pressure vessel is determined by subtracting the distance from which the gauge originally protruded from the core tank from the reading of the dial gauge. The length of the energy absorber 85 is then adjusted accordingly as part of the individual adaptation shown in step 102 of FIG.

After removing the old lower furnace internals,
Processing of the furnace internals must be performed. Therefore,
According to the present invention, in step 95, the old lower core structure is returned to the reactor cavity after alignment measurements are performed on the new lower core structure in step 92. Accordingly, the processing operation can be performed in step 102 in parallel with the individual adaptation of the new reactor internals. As shown in FIG. 13, the old lower reactor internal structure is
After returning to 4, the core tank 5 is supported by being separated from the flange 57 of the pressure vessel by a support stand (preferably three support stands 55) attached to the flange. Alternatively, the core vessel 5 may be
Could be suspended from a beam of I-shaped cross-section disposed at the top of the beam. According to the present invention, step 88
The reactor cavity 54 is flooded to a water level 86 such that the water depth 87 above the pressure vessel flange 57 is greater than the length of the core vessel 5. Therefore, the entire core tank 5 is supported above the flange of the pressure vessel.
Is located entirely underwater.

In step 96, the processing of the heat shield 6 is performed first. The reactor core tank 5 has a reactor cavity 54.
In the state of being immersed in the inside, four longitudinal cuts are formed in the heat shield 6, and the heat shield 6 is cut into four arc-shaped portions. Next, the heat shield is cut in the circumferential direction to form eight arc-shaped portions that can be appropriately stored in the disposal cask. The cutting of the heat shield 6 in water may be performed by using a plasma arc method.

After removing the heat shield 6, step 97
, The old lower reactor internal structure is moved from a position above the pressure vessel 1 into a submerged storage stand (not shown) in the reactor cavity 54. Thus, the new lower furnace internals that have been individually adapted in step 102 are returned to the pressure vessel 1 so that they can be verified for achieving proper alignment. If this is not the case, but the new lower core structure is incompatible, the old lower core structure, without the heat shield, is reinstalled and the reactor is inserted after refueling for the next operating cycle. Can be returned to the operating state. In that case, the new lower furnace internal structure is reworked. In this way, by removing the heat shield in parallel with the individual adaptation of the new lower furnace internals, the time required for removing the heat shield is not added to the time required for the important method. Furthermore, this scheduling advantage is realized without the danger of delays in returning the reactor to service in a timely manner, even if unexpected problems arise in the customization operation.

After verifying the alignment of the new lower internal structure, the new lower internal structure is again removed from the reactor cavity 54 in step 99, and the old lower internal structure without the heat shield 6 is removed in step 100. To the reactor cavity, and again, as shown in FIG.
7 support. In step 101, the old core tank 5
Is cut into at least three parts by a series of cuttings in the circumferential direction. In a preferred embodiment, the cut is made just below the outlet 73 and just above the lower core plate 9. Since the lower part of the lower core plate 9 is the heaviest part, depending on the capacity of the crane, further cutting at this part may be necessary. Each part is then placed in a flooded treatment cask.

After treating the old lower reactor internal structure in step 101, the reactor cavity 54 and the pressure vessel 1 are cleaned, and the new lower reactor internal structure is reinstalled in the pressure vessel as a final assembly step in step 103. Recheck the alignment in this final step.

Although the preferred embodiment of the present invention has been described above, the present invention can be embodied in other specific forms without departing from the concept or essential attributes thereof. It should be noted that the interpretation of the present invention should be based not on the above description but on the description of the claims, and also to refer to the description of the following items in addition to the claims. I do.

The method of any preceding claim, further comprising the step of: (A) using a simulated replacement lower core assembly to remotely measure a predetermined alignment of the replacement lower core assembly. method of exchange. (B) the first position alignment means includes a plurality of mating pairs of first and second position alignment members, the first position alignment members being distributed along an inner surface of the pressure vessel. Measuring the position alignment of the new lower internal structure assembly with respect to the pressure vessel, wherein the second alignment member is distributed along an outer surface of the lower internal structure assembly. 3. The method of claim 2, further comprising the step of: determining the position of the second alignment member on the new lower core internals assembly required to achieve the predetermined alignment. (C) the first position alignment means includes a key adapted to engage a keyway formed in the pressure vessel, and position alignment of the new lower internal structure assembly with respect to the pressure vessel. 3. The method of claim 2 wherein measuring the position of the key comprises measuring the position of the key on the new lower core internals assembly required to achieve the predetermined alignment. (D) measuring the position of the key; a) securing a gauge in place of the key to the new lower internal structure assembly; and b) compressing the new lower internal structure assembly to the pressure. The replacement method according to the above (C), comprising a step of installing the keyway in a container, and a step of measuring a distance from the gauge to the keyway. (E) A replacement method, wherein a side surface is formed in the keyway, and the gauge has a plunger that can be extended and retracted, and a) installing the new lower furnace internal structure assembly in the pressure vessel. (D) using the plunger in a retracted position, and b) further comprising extending the tip of the plunger until the tip of the plunger contacts one of the sides of the keyway. Exchange method. (F) The step of forming the first position alignment means so that the predetermined position alignment is achieved includes the step of grinding the key based on a distance from the gauge to the key groove. The method described in the section. (G) the nuclear reactor includes: (i) a core containing a fuel assembly; (ii) control rods; and (iii) an upper core structure assembly adapted to guide the control rods; The core and the upper core structure assembly are enclosed in the pressure vessel, and the new lower core structure assembly and the upper core structure assembly move the new lower core structure assembly to the upper part. Second and third alignment means for aligning with the in-furnace structure assembly, respectively, further achieving predetermined alignment of the new lower in-furnace structure assembly with respect to the upper in-furnace structure assembly; 3. The method according to claim 2, further comprising the step of positioning said second position alignment means on said lower in-core structure assembly. (H) the third position aligning means includes a notch formed in the upper in-core structure assembly, and the step of positioning the second position aligning means includes the step of positioning the notch with respect to the fuel assembly. The exchange method according to the above (G), comprising a step of measuring a position. (I) the upper core assembly further includes: a first pin for each of the fuel assemblies; and a first hole formed in the upper core assembly for each first pin. Wherein each of said first pins is disposed in a respective first hole, and further comprising the step of measuring a position of said notch relative to said fuel assembly, said step of measuring said notch relative to one of said first holes. The replacement method according to the above (H), including a step of measuring a position of the notch. (J) measuring the position of the notch with respect to one of the first holes includes attaching a gauge to the upper furnace internals assembly and positioning the gauge using the first pin. The exchange method according to the above (I), comprising: (K) The replacement method, wherein the notch has a side surface, and the gauge has a plunger tip that can be extended and retracted, a) attaching the gauge to the upper furnace internal structure assembly, A gauge is inserted into the notch so that the plunger tip is on one side of the side of the notch.
B) measuring the position of the notch relative to one of the first holes from the plunger tip to the first position.
(J) The method according to the above (J), comprising the step of measuring the distance to the hole. (L) positioning the second position alignment means on the lower internal structure assembly such that the predetermined position alignment is achieved, further comprising: a dummy upper furnace having a plurality of second holes. Providing a reference point on the internal structure assembly, wherein the position of the reference point relative to one of the second holes is the same as the position of the notch relative to one of the first holes; The replacement method according to the above (I), wherein the position of the second hole with respect to the internal structure assembly is related to the position of the first hole with respect to the upper internal structure assembly. (M) the second position alignment means includes a second pin arranged in a third hole provided in the lower in-core structure assembly and adapted to engage with the notch; ,
Positioning the second position alignment means on the lower core structure assembly such that the predetermined position alignment is achieved, comprising: a) the dummy upper core structure on the lower core structure assembly; The method of claim (L), further comprising: installing an object assembly; and b) drilling the third hole along a radial line passing through the reference point. And (N) means for moving said plunger coupled to said plunger and disposed within said bore.
A position alignment device as described in the above. (O) The position alignment device of (N), wherein the means for moving the plunger includes means for receiving a voltage, and responsive to the received voltage. (P) a pressure vessel surrounding the core vessel, the core vessel containing a core plate and a plurality of fuel assemblies, a cutout formed in the core plate, and a first hole in the core plate; A first pin for each of the fuel assemblies disposed therein, wherein the core vessel is disposed within a second hole formed in the core vessel to enter the notch. 4. The reactor of claim 3 having a second pin having a first hole having a third hole spaced apart from and corresponding to the first hole. B) a second portion adapted to enter the notch; and c) to position the core vessel relative to the core plate disposed within the second portion. And a notch position display means for displaying a position of the notch with respect to the third hole. (Q) The position alignment device according to the above (P), wherein the notch position display means includes a movable plunger.

[Brief description of the drawings]

FIG. 1 is a vertical sectional view of a nuclear reactor.

FIG. 2 is a cross-sectional view taken along line 2-2 shown in FIG.

FIG. 3 is a plan view of the upper core plate shown in FIG. 2 near an alignment pin.

FIG. 4 is a plan view of a dummy upper core plate installed in a new core tank.

5 is a plan view of the upper core plate shown in FIG. 3 as viewed from below, with the alignment pin hole detection gauge installed.

6 is a cross-sectional view taken along line 6-6 of FIG.

FIG. 7 is a cross-sectional view taken along line 7-7 shown in FIG. 5;

FIG. 8 is a cross-sectional view taken along line 8-8 shown in FIG.

FIG. 9 is the same as FIG. 8 except that a radial support key alignment gauge is installed.

FIG. 10 is a vertical sectional view in the vicinity of a lower portion of the pressure vessel and the core vessel, showing a length measuring gauge of the energy absorber.

FIG. 11 is a perspective view of the radial support key alignment gauge shown in FIG. 9;

FIG. 12 is a sectional view taken along line 12-12 shown in FIG. 1;

FIG. 13 is a vertical sectional view of a containment vessel of a nuclear power plant, showing a reactor core vessel disposed above a reactor vessel in a reactor cavity.

FIG. 14 is a flowchart showing steps for replacing a lower internal structure of a nuclear reactor.

FIG. 15 is a partial elevational view of a simulated lower in-core gauge in the reactor pressure vessel shown in FIG. 1;

16 is a cross-sectional view of the simulated lower in-core gauge at line 16-16 in FIG.

FIG. 17 is a partial elevational view of the simulated lower internals gauge of FIG. 15 disposed on a stand external to the reactor pressure vessel.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Pressure vessel, 2 ... Lid, 3 ... Control rod drive shaft, 4, 60
... pillars, 5 ... core tank, 6 ... heat shield, 7 ... fuel assembly alignment pins, 8 ... upper core plate, 9 ... lower core plate,
DESCRIPTION OF SYMBOLS 10 ... diffuser board, 11 ... bottom part, 12 ... energy absorption board, 13 ... instrumentation thimble guide, 14 ... fuel assembly,
15 inlet nozzle, 16 outlet nozzle, 17 baffle, 18 upper core plate alignment pin, 19, 7
5, 76: Notch, 20: Insert, 21: Dummy core plate, 22: Alignment pin hole, 23, 66, 83
... Center line, 24, 42, 44, 74, 79 ... Hole, 25,
34, 42: alignment pin gauge, 26: fuel assembly alignment pin hole, 27: leveling pad, 28
... tongue, 29, 43 ... plunger, 30 ... set screw,
32 ... radial direction support key, 33, 78 ... screw, 34 ... dwell, 35 ... key groove , 36 ... insertion member, 37 ... boss , 3
8 boss , 39 mounting pad, 40 radial support key gage, 41 linear voltage operated transformer (LVDT), 4
6 ... gauge, 47 ... scratch gauge, 48 ... dial gauge, 49 ... underwater television camera, 50 ... lid /
Pressure vessel alignment pin, 51: radially extending portion, 52: control rod guide tube, 54: reactor cavity,
55: trapezoidal portion, 56: control rod support plate, 57: flange of pressure vessel, 58: core tank flange, 59: flange of control rod support plate, 61, 62, 63, 64 ... side portions, 69, 8
1 ... Dwell hole, 70 ... Former, 71 ... Core, 72 ...
Cylindrical part, 73 ... outlet, 76 ... gap, 76 ... keyway of pressure vessel, 77 ... press spring, 79 ... alignment pin hole, 80 ... base, 82 ... spring, 84 ... dummy fuel assembly alignment pin, 85 … Energy absorber, 86…
Water level, 112 ... simulated energy absorber substrate,
115, 116 ... simulated outlet connection, 140
... Gauge block, 150 ... Gauge pin, 200 ... Simulated lower furnace internal structure gauge, 202 ... Main frame, 206,210,214 ... Horizontal member, 208 ... Upper plate assembly, 212 ... Intermediate plate assembly, 216 ... Lower plate assembly, 220: hollow central column, 222: vertical member, 230
... vertical pillars, 232, 234 ... large diameter part, 236 ... storage stand.

──────────────────────────────────────────────────続 き Continued on the front page (72) Leonard J. Barog, Inventor Georgetown Drive, Export, Pennsylvania, United States of America 205 (72) Ronald J. Hopkins, Inventor United States, Florida, Pensacola, Strass Berg Road 8270 (72) Inventor Arthur W. Kramer General Forbes Road, Genet, Pennsylvania, United States 1013 (72) Inventor Donald G. Sherwood United States, Pennsylvania, Monroeville, Lilac Drive 249 (58) Field surveyed (Int. Cl. ⁷ , DB name) G21C 19/02

Claims (3)

(57) [Claims] 1. A method for replacing an already used lower core structure assembly in a reactor pressure vessel with a replacement lower core structure assembly, wherein a first position alignment means is to be formed. in position, the exchange and the exchange lower internals assembly comprising the steps of remotely measuring the position of alignment with the reactor pressure vessel, and the reactor pressure vessel on the basis of measurements of the remote position alignment Forming the first position alignment means so as to obtain a predetermined position alignment with the lower furnace internal structure assembly. 2. A new lower core structure assembly comprising a pressure vessel and old and new lower core structure assemblies surrounded by the pressure vessel and adapted to support a core assembly. Comprises: a reactor having first alignment means for aligning the new lower internal structure assembly with respect to the pressure vessel, wherein the old lower internal structure assembly is replaced by the new lower internal structure assembly; (A) a position where the first position alignment means is to be formed;
The lower furnace of the New and measuring the position alignment of the lower internals assembly of the Xin remotely, to said pressure vessel based on the measurement of the (b) said remote position aligned with respect to the pressure vessel in Forming the first alignment means so that a predetermined alignment of the internal structure assembly is achieved. 3. A pressure vessel surrounding the core vessel, wherein the pressure vessel has a keyway formed therein, the core vessel having a key adapted to enter the keyway, and a keyway associated with the key. A reactor having mounting pads that are
An apparatus for aligning said core vessel with respect to said pressure vessel, comprising: (a) a first portion and a second portion, wherein said first portion has a hole formed therein and said A gauge adapted to fit into the keyway and a second part adapted to mate with the mounting pad; and (b) a plurality of movable plungers disposed in the bore. (C) The core tank position alignment device, wherein the hole is formed in the first portion so that tips of the plurality of movable plungers can contact both sides of the keyway.